To rapidly cool products, the food industry has increasingly turned to vacuum cooling processes. These vacuum systems can be used to cool various food products in a fraction of the time necessary with conventional methods. Such systems are particularly useful for cooling milk. In such a system, a vessel filled with milk is quickly cooled when exposed to an increasing level of vacuum. However, in such a process, when the level of vacuum reaches approximately 10 mm of mercury, a milk foam begins to form on the top of the liquid. As the vacuum level increases, the foaming action accelerates to the point at which the upper part of the vessel becomes completely filled with foam. The foam is then drawn into the piping leading to the vacuum equipment, thereby fouling the vacuum lines. This piping must then be disassembled and cleaned, a very time-consuming process.
To prevent this foaming, it has been suggested that food companies control the level of vacuum. To achieve such control, an operator must watch the milk cooling process and, when foaming is detected, prevent the level of vacuum from increasing further. This has been done by opening a valve, which caused bleeding of atmospheric air into the vacuum system. The disadvantage of this method is that the cooling process is lengthened, and an operator must observe the entire process. Therefore, methods of automating this process have been desired.
One solution to the foregoing problem would be to install a control valve to bleed in a set rate of air at a specific time relative to the product being cooled. Alternatively, a level detector, sensitive enough to detect foaming, could be installed to signal the control valve to bleed in air when foaming occurs. The disadvantage to any such control valve set up, however, is that the initial expense is greater and, a slower cooling cycle occurs due to the air which is bled into the system.